Archbishop of Canterbury the Rt. Rev. Justin Welby is set to meet on Thursday with gay rights campaigner Peter Tatchell, who insists that Christians who are opposed to same-sex marriage are homophobic.

"I applaud the Archbishop's willingness to engage in dialogue – all the more so because he comes from the conservative evangelical wing of the church," Tatchell said, according to San Diego Gay and Lesbian News. "I hope our meeting is not mere window-dressing and good PR for the church. I'm expecting more than tea and sympathy."

In response to a letter by Tatchell accusing the Anglican leader of being homophobic for supporting traditional marriage, Archbishop Welby replied: "Dear Mr Tatchell, Thank you for your very thoughtful letter. It requires much thought and the points it makes are powerful. I would like to explain what I think to you without the mediation of the press, and listen to you in return."

Welby recently said that his stance on gay relationships has been challenged by the love and commitment he has seen his gay friends display, but backed the official Anglican position that marriage is solely between a man and a woman.

"The Church of England holds very firmly, and continues to hold to the view, that marriage is a lifelong union of one man to one woman," Welby has said. "At the same time, at the heart of our understanding of what it is to be human is the essential dignity of the human being."

In a letter written in March, Tatchell, who is a well-known Australian-born British political campaigner, insisted that Welby and Christians who defend the traditional definition of marriage are being homophobic, regardless of whether they accept that label or not.

"You claim that you are not homophobic but a person who opposes legal equality for LGBT people is homophobic – in the same way that a person who opposes equal rights for black people is racist," the gay rights leader wrote to Welby.

"Homophobia has come to mean more than an irrational fear for gay people. It includes support for anti-gay discrimination and the denial of equal rights to people who are LGBT. In this sense of the word, you are homophobic because you support discrimination in law against gay people," he added.

Tatchell, who is an atheist, argued that discrimination, to which he equates supporting the traditional definition of marriage, is not a Christian value and should not be embraced by its leaders, regardless of long held beliefs.

"This is the first time any Archbishop has offered to meet me. Even a liberal like Rowan Williams never welcomed me to Lambeth Palace. Justin's invitation is progress," he said, praising Welby.

While both the Anglican and Catholic churches in England have opposed gay marriage, the British government remains committed to legalize the practice by 2015.